My
address decoding circuits design incorporated Phi2 signal in the
decoding scheme. I consulted literature and expertise of
knowledgeable people on the 6502 subject and decided this is not the correct approach. I removed the Phi2 signal from address decoders
input. The Phi2 signal is now only used to synchronize
reading/writing access cycles.

I
tested two variants of RTC circuit:

and
decided to go with 2-nd one (seems to be more reliable and less
susceptible to problems resulting from long propagation times).